1. Field
The field is suction dredging apparatus, in particular dredging apparatus that resists clogging.
2. Prior-Art Dredging Apparatus
There is no admission that the background art disclosed in this section legally constitutes prior art.
There have been a variety of different kinds of dredge type equipment proposed for gathering materials. For example, reference may be made to the following U.S. Pat. Nos. 3,664,768; 3,964,123; 4,499,713; 4,884,392; 4,889,391; 5,408,766; 5,425,188; 5,487,229; 5,592,805; 5,621,945; 5,791,073; and 6,112,439.
Water suction dredging may be considered to be a system of mining that may involve the balancing of several features including a power source for driving a water pump that takes in water through a first hose and sends it out under pressure through a second hose. The second hose delivers the water under pressure to a nexus containing a suction head feature which joins the intake and exhaust hoses and an opening used to recover by suction material from a body of water such as a river bottom. The recovered material may be carried out by a third hose and delivered to a sorting station.
Several human operators may be required to monitor aspects of the system and the work environment. In small river mining operations, for example, a single human operator may perform some or all of these activities. In larger operations, one human operator may direct the suction head intake orifice (or nozzle) to the material to be taken into the system. That human operator may regulate the proportional flow of material-to-water to be taken into the system. It may be the operator's responsibility to clear fouls as they occur so as to maintain the steady flow of the dredging activity.
Suction dredge intake heads may be a short rigid tube with one or more handles attached. There may be several holes such as four holes (three external) in the head: a first hole for the pressure intake hose, a second hole for the carrier exhaust hose, a third hole for the intake orifice that receives the dredged material, and a fourth internal hole where the pressure intake hose and materials drawn in at the intake orifice combine to enter the exhaust hose.
Each dredge intake head may have an intake opening or orifice in which water and materials to be dredged enter. A human operator may direct the orifice of the dredge head onto the material to be recovered by the system, and may regulate the flow rate of materials by moving the head opening away from the material to free water occasionally if the collection rate is deemed too rapid. A flow rate of water-to-material of nine to one may, for some applications, be considered appropriate to prevent fouling at the intake head or within the exhaust carrier hose that transports the slurry back to a material collection station. Best practices may employ a second water pump in series to maintain pressure in the system all the way to the screening station.
Suction dredge intake heads may become blocked when the human operator allows a too rapid accumulation of materials, such as algae, kelp, or gravel, in a water environment, to enter the intake orifice, or by the attraction of a single large object such as a rock that blocks the entry orifice. The result of a blockage may be the rapid loss of pressure in the exhaust hose causing the dredging to stop until the blockage is cleared. Hence, there may be a loss of productivity.
A probe may be used to free the blocking materials, such as by poking in from the front. However, there may be the possibility that the tool, or the operator's hand, may be sucked into the dredge when the foul is cleared. Manually clearing fouls thus may be dangerous, under certain conditions, to the human operator, as well as being destructive to expensive equipment.
Many factors may limit dredging efficiency. These factors may include the length of hoses, the occurrence and severity of bends in the hoses, the relative internal roughness of the hoses and fittings, the types and tightness of couplings employed, and the design of the Watergate and sluice box. Modern materials, such as high strength polymer suction hoses, efficient pumps, and light weight engines have greatly enhanced for at least some applications, the efficiency of the small dredging operation.
There is a need in certain applications to balance the dredging system because it may be desirable to balance the power of the engines and pumps against the ability of the operator to handle the equipment safely and efficiently. Also, another factor which may be considered is the capacity of the raft being used to support the volume arriving at the material recovery station. The weight of the engines, pumps, and sluice table, if it accumulates yards of material, may overburden the floats of the raft.
A single, experienced operator, with a dredge, may collect many times more material than could be processed by hand collection methods. For example, a six inch (15.2 cm) dredge, in experienced hands, may process approximately twice as much material as can be accomplished with a 4-inch (10.2 cm) dredge. An 8-inch (20.3 cm) dredge may about double the production over a 6-inch (15.2 cm) dredge. A 10-inch (25.4 cm) dredge can double production over an 8-inch (20.3 cm) dredge.
In the larger dredges, there may be a danger inherent in the larger scope of activity including the requirement for more personnel in the operating area to assist in moving obstacles to the dredge operator's access to targeted material. There may also be a need for vigilance during production so as not to input too much material at the head too quickly that it causes a blockage, or to have an operator's or assistant's body part sucked into the equipment while attempting to clear the blockage. Safety is, of course, important in the operation of such equipment.
Generally, the blockage at the head slows down the production of dredgers. The volume of material that is sucked up the nozzle in any given location may determine production. Volume momentum may be lost every time the operator has to clear a blockage manually, and safety is always a concern.
In the history of the development of suction dredge technology there may be a correlation between the changing source of suction power and the shape of the dredge head nozzle. The dredge usually functions on the same principle, independently of the power source. In this regard, the principle of operation of conventional dredges may relate to the use of a vacuum created by the Venturi effect. A siphon from the movement of water in a pipe, hose, or tube, may create a negative pressure that pulls the water and other materials through the nozzle intake opening, through the exhaust hose, and delivers it to the collection station or sluice.
In ancient times when the source of the suction power may have been from gravity pulling water through a tube, whether rigid as an iron pipe or flexible as a fire hose, a straight suction dredge nozzle may be attached to a short carrier hose inserted anywhere at or below the point where the suction was considered adequate to remove the targeted material. The combination of the intake water and dredged slurry material may be carried through by suction to the exhaust portion of the tube, and may then be deposited in a location below that point on a vertical scale where the sorting of the material took place. Typically, the slurry borne material may mechanically be deposited onto an artificial alluvial plane. When the water entered the plane and spread out, the decrease in pressure resulted in deposit of the material with the greatest specific gravity, such as gold, close to the exit point, while the lighter, less valuable dross debris carried further. Thus, the material closest to where the exit hose made its deposit may have been examined most closely by the miner for valuables.
When the miners may have been using gravity flow as the power for the dredging, the location of the intake of the water at the beginning of the process may have been a distance from the point of deposit of the materials dredged. The distance might be great both on the vertical and horizontal geographic planes. Hence, the side entry tube configuration may have been straight and entered the main current of the flowing water obliquely at a slight angle so as to attempt to maintain the largest possible suction. Calculations may have shown that the degradation of suction that occurred as the angle of intercept moved away from the main flow of the water. The closer the angle approached unity as the cosine of angular separation of their central axis, the greater the force of the suction. Thus an angle of 30 degrees separation may have a higher cosine than 45 degrees, thus the 30 degrees may be better.
On relatively level ground, where gravity flow systems may not have been practical or possible, the steam engine came into its own as the source of pump power and these areas may have then become workable. At least at first no change in nozzle head design may have been required. The steam engine may have been located at one place on a river bank and further down stream could be the location of the alluvial plain for the recovery of dredged materials. The dredge head could still be essentially straight in configuration.
Eventually, internal combustion engines operating on methane, ethanol, gasoline, or diesel took over from steam as the source of power to drive the water pump. Electric pumps could also be used of course. What remained was the idea that the source of water being drawn into the system did not have to be in the same location as the place where the dredged material would be deposited for sorting. When miners built their own dredges, there may not have been the need to change from the original head design as being essentially a straight tube intersecting the suction hose at a shallow angle leading into the exhaust hose.
The shape of the suction head may have changed only as a matter of convenience when a portable power source made the recreational gold dredger the dominant feature in the gold fields. Anywhere a portable dredge may be transported and entered into the water of a stream, miners may have set an engine, water pump, hoses, and a sluice box on a single floatation device which they would anchor somewhere in one location to work the streambed gravels directly below. If the location was changed, the whole flotation may have been moved to the new location. Hence, the source of power to the suction dredge system may have been at, or was almost at, the same location as the sluice box for the material recovered. Now the hoses of the system, both sending pressure hose and receiving exhaust hose, were at almost the same place, floating on the same flotation device, and so the suction dredge head of the operation became modified in numerous variations often only aesthetic.
This modification from being a straight pipe intersecting a straight pipe in a shallow V shape, may have evolved to being curved like a U or perhaps a lower case h, may have been an artifact of the relocation of the hoses both sending and receiving, and was not necessary other than for convenience. The commercial dredge manufacturers accommodated the expectations of their customers and constructed dredge heads in the U or h shape, although there may have been variations in length of the solid tube and it may have had multiple handles, and support mechanisms between the end units where the sending and receiving hoses intersected.